Past continuous or past simple?

Past continuous = I was working Past simple = I worked

Choice of emphasis

Often there is little difference between the past continuous and the past simple, except that the past continuous suggests that the event(s) were in progress at a time in the past or that they were happening as background or temporary events. Whether we choose to use the past continuous or past simple often depends on how we see the past event(s).

Compare

Doctors were treating patients in temporary beds and they were trying to do their best in a difficult situation.	Past continuous: writer chooses to show the events as ongoing at that time in the past.
Doctors treated patients in temporary beds and they tried to do their best in a difficult situation.	Past simple: writer chooses to show the events as finished.

Events in progress in the past

We use the past continuous to talk about events and temporary states that were in progress around a certain time in the past. We use the past simple to talk about events, states or habits at definite times in the past.

Compare

At 4 pm last Tuesday, I was working in the office.

The past continuous emphasises the action or event in progress around a time in the past. The event (working) was in progress at 4 pm.

The event was not completed at that time.

At 4 pm last Monday, I finished work early and went home.

The past simple emphasises the event that happened at a definite time in the past.

The focus is not on events in progress but rather on the whole events (finished work, went home).

The events were completed at that time.

Emphasising main events with the past simple

When one event is more important than the other in the past, we can use the past simple to emphasise the main event. We can use the past continuous for the background event (the less important one):

[background event]I was listening to the radio when [main event]Helen phoned.

[background event]I was sitting in the park and suddenly [main event]I saw an old school friend I hadn’t seen for 30 years.